Poly alkyl methacrylate pour point depressants are well known in the lubricating industry. Many attempts have been made to produce poly alkyl methacrylate pour point depressants that improve the low temperature viscometrics of various lubricating compositions.
Pour point depressant (PPD) additives improve the low-temperature performance of an oil by modifying the wax crystallization process. A wide variety of chemical types are currently available, and include poly alkyl methacrylates, styrenated polyesters, alkylated polystyrenes, ethylene-vinyl acetate, vinyl acetate-fumarate, esterified olefinic, styrene maleic anhydride, and alkylated naphthalenes. The present invention is directed to alkyl methacrylate polymers which exhibit desired low temperature properties. More specifically, the invention is directed to PPDs that exhibit outstanding low temperature properties in lubricating oils for applications such as automatic transmission fluids, manual transmission fluids, hydraulic fluids, greases, gear fluids, metal-working fluids, engine oil applications, crankcase motor oil and shock absorber fluids. The oil chemist is constantly searching for PPDs that achieve optimum low-temperature performance at low concentrations. The present invention addresses the need for an improved PPD.
In particular, the invention addresses the need for a pour point depressant which can be used in a variety of oils at lower treat rates, displays less interactions with other components of the oil such as dispersants and inhibitors, shows stability in shear fields and lower gelation indices in some instances depending on the base oil than for previous pour point polyalkylmethacrylates. It is also important that the PPD be soluble and compatible with the base oil and maintain an appropriate BROOKFIELD viscosity at low temperatures. Incorporation of the inventive poly alkylmethacrylates is shown to do just this; addition of the inventive poly alkylmethacrylates gives improved viscosity at low temperatures while maintaining acceptable pour point depressant activity.
U.S. Pat. No. 2,655,479 to Munday et al. claims a pour point depressant composition consisting of a blend of two copolymers, the first copolymer having an average side chain length of about 12.7 while the second copolymer has an average side chain length of about 11.2.
U.K. Patent No. 1,559,952 discloses a mixture of two classes of oil soluble poly alkyl methacrylates as pour point depressants.
U.S. Pat. No. 4,146,492 discloses lubricating oil compositions comprising between about 0.5 and 30 wt. % of a specifically defined ethylene-propylene copolymer and between about 0.005 to 10 wt. % of a neat interpolymeric poly alkyl acrylate of (A) C1-C15 alkyl acrylate and (B) C16-C22 alkyl acrylate having a weight ratio of A:B of between about 90:10 and 50:50, a molecular weight of from 1000 to 25,000 and an average alkyl side chain length of between about 11 and 16 carbons.
U.S. Pat. No. 4,867,894 discloses pour point improving additives for mineral oils comprising from 10 to 30 mole percent methyl methacrylate, 10 to 70 mole percent of a linear C16 to C30 alkyl methacrylate, from 10 to 80 mole percent of a C4-C15 linear alkyl methacrylate and/or a C4 to C40 branched methacrylate, and from 0 to 30 mole percent of a free-radically polymerizable nitrogen-containing monomer having dispersing action.
U.S. Pat. Nos. 5,312,884 and 5,368,761 disclose copolymers useful as pour point depressants for lubricating oils comprising 15-67 mole percent C8-C15 alkyl (meth) acrylates, 3-40 mole percent C16-C24 (meth)acrylates, and from greater than 30-65 mole percent C1-C4 methacrylates. These patents do not teach copolymers containing the specific monomers in the specific proportions required by the present claims.
U.S. Pat. No. 5,281,329 discloses copolymers useful as pour point depressants for oils containing at least two species of poly alkyl (meth)acrylate, one species having an onset of crystallization temperature above 15° C. and one species having an onset of crystallization temperature below 15° C.
U.S. Pat. No. 5,534,175 discloses copolymers of unsaturated fatty esters derived from 12-20 mass % of a C1-C3 (meth)acrylate, 45-72 mass % of a C11-C15 (meth)acrylate and 14-30 mass % of a C16-C25 (meth)acrylate.
EP 0 236 844 B1 teaches pour point improving agents derived from methyl methacrylate.
U.S. Pat. No. 6,255,261 discloses copolymers formed from 5 to 60 weight percent C11-C15 (meth)acrylates and 95 to 40 weight % C16-C30 (meth)acrylates for use as pour point depressants.